Compression Techniques

File Format Compression Techniques

There are two compression techniques used for bitmap file formats; lossy and lossless.

Lossy compression is when quality is sacrificed for image size. This is done by reducing the amount of information in the picture to create a smaller version. Usually, a lot of the information can be removed without it being distinguishable from the original because the human eye can't perceive the fine details that were removed during the process. If a file is compressed too much, the image is smaller in size but clearly of a lower quality than the original. JPEG is the most popular format for lossy compression because it can make an image size very small without too much loss of quality.

Lossless compression allows the exact image to be reconstructed from the compressed data. This means there is no loss in quality at all but the file size is considerably larger than that of a image created using lossy compression. The algorithms used for lossless compression attempt to compress the image as much as possible without losing quality. Certain algorithms are slower but more effective than others. This is because they have to analyse all the data in the picture while trying to find patterns that can be saved.

Compression is done by using an application such as WinZip but there are lots of other applications for compressing including WinRAR, 7-Zip, PeaZip etc.

These applications allow you compress any amount of files into a single folder or archive which can then be "unzipped" to decompress the data and use the files again. There are several options when compressing data such as how fast you want the folder to compress. If you set the folder for a fast compression, it will not compress the folder or file as well as it could if it was set to maximum compression.

Lossy Compression

Advantages

Smaller file size than lossless compression

Even though it sacrifices data, it is usually data that is barely distinguishable to the human eye anyway

Disadvantages

Sacrifices data at the cost of image quality

Can produce artifacts due to the compression

Lossless Compression

Advantages

Doesn't lose any data at all during compression but size is made slightly smaller

Disadvantages

Produces larger file size than lossy compression

My Compression Screencast